RU2003928C1 - Method of control over tubular furnace - Google Patents

Description

However, this method does not allow a sufficiently accurate optimization of the combustion process because it is achieved by changing the air flow and the position of the smoke damper, following the limitations on the oxygen content. The latter, as a result of possible suction and other disturbance factors, can vary regardless of the combustion mode of the fuel. In addition, with excess oxygen exceeding a certain minimum limit, nitrogen oxides begin to intensively form, which degrade the ecological environment.

This, like all of the control methods described above, makes no guarantee that during the control process an excess of oxygen in the flue gases will be minimally necessary.

An object of the invention is to improve the accuracy of optimizing the combustion mode of a fuel.

The goal is achieved by the fact that according to the proposed method of controlling a tube furnace by adjusting the rate of supply of fuel gas to the combustion chambers, adjusting the vacuum by removing flue gases and optimizing the combustion process based on the measurement of oxygen in the flue gas and controlling the air flow through the chambers, the content is additionally measured hydrogen or products of underburning in flue gases and in specified restrictions minimize the value of the function:

R H2 + 102, (1)

where H2, 02 are banners of altered concentrations of hydrogen (products of underburning), oxygen in flue gases; I am the coefficient, changing first the total air supply, then the distribution over the chambers.

The value of the coefficient H depends on in which units the iodorode and oxygen contents are measured by gas analyzers. If the indicated parameters are measured in mass units, for example, in mass percent, then the value of берет is taken in the range of 0.076 ... 0.106. These values of I were obtained on the basis of the following reasoning. The calorific value of gaseous molecular hydrogen is 142324 kJ / kg, the calorific value of hydrogen, which is part of the fuel compounds, is 125580 kJ / kg. The calorific value of hydrogen in the calculation of the lower calorific value of the fuel, i.e. taking into account the heat consumed by the evaporation of water generated during the combustion of hydrogen, is equal to 102828 kJ / kg.

The decrease in the calorific value of the fuel due to combustion when the oxygen content in the combustible mass of the fuel is calculated by D.I. Mendeleev approximately 5 is 10883.6 kJ / kg. To balance the contributions of hydrogen and oxygen contained in the products of combustion, the readings of the oxygen meter should be reduced to 142324 / 10883.6 ... 102828 / 10883.6, i.e. at

0 13.077 ... 9.462 times (I -0.076 .... I 0.106). If both gas analyzers give the content in volume units, for example, volume percent, then with the same volumes of hydrogen and oxygen, the amount

5 oxygen will be 8 times the mass.

Thus, the value of the coefficient I should be further reduced by 1 in the 8th groove, and then its value will be 0,0108 .... 0,0132,

0 An essential feature of the presumptive method is the introduction of function (I) in the method of controlling the combustion mode and supplying air to the chamber. It is this feature that will give the method an existing novelty and a number of new properties.

The main reactions occurring at the end of the process of gas fuel synthesis are described by stoichiometric equations i:

0H2 (- 0.502 NoO (2)

CO h - 0.5 0l CO2

In a thermal ratio, both oxidation reactions are approximately equivalent

Since combustion occurs due to oxygen in the air, nitrogen added with air is added to the reaction part (2)

79

N2 - from 02. Yes, a file with the completion of reaction (2) requires a significant excess

0 air, but with an empty process, the efficiency of the process will decrease, since it will require additional heat to heat it. Conversely, when there is a lack of freezing sound about the result of a shift in the equilibrium of reaction (2), the efficiency is

5 is reduced due to the npv sutsteis of the product / combustion of significant quantities of hydrogen and carbon monoxide. Therefore, to conduct process g; about the optimal mode in terms of efficiency, the presence of oxygen,

0 of hydrogen and carbon monoxide in some of the minimals. But it is obligatory. Minimization of function (1) allows us to achieve the lowest efficiency, for example, by defining a surprise in the product) and

5 simultaneous mini ;; oxygen S of a given BSGiiatre hydrochloride in petm and an indicator of the simultaneous existence of OKHCV carbon

The implementation of the process according to the pre-proposed method does not allow developing the desired reactions of the formation of nitrogen oxides, since the content of hydrogen (although in a small amount) as a more active component with respect to oxygen suppresses the processes of oxidation of air nitrogen. Even at zero hydrogen content, the system implementing the method will reduce the oxygen content, which also contributes to the suppression of oxide formation reactions. A similar effect cannot be achieved using previous methods of controlling the combustion process, as soon as we do not separately analyze nitrogen oxides and control the process to minimize them.

The implementation of the method can be carried out with manual control, calculating function (1) according to the analyzer and wire permutation of the regulating body of the air supply.

However, the efficiency of the method is greatly increased if a special automatic control system is used. An example of such a system is shown in the drawing.

In essence, this system is a modification and development of the system of prototype 5. The system can be implemented on the basis of a control microcomputer. However, in order to clarify the principle of interaction between computing units, a functional block diagram is provided.

The tubular furnace P has two chambers, in each of which the product is heated by a coil circulation process. & chambers burn gaseous fuel. Air is supplied from a common air duct by a blower B. Each chamber is equipped with an exhauster E operating on a common chimney T. The required vacuum value in each chamber is supported by an individual automatic control system consisting of a pressure sensor 1, element 2 for comparing the measured pressure with a given P , regulator 3 and actuator 4 with action on the flue gas exhaust system. In principle, if the chambers are in good communication with each other, then one regulator can be dispensed with choosing one characteristic pressure sampling point. The supply of fuel gas to each of the chambers is carried out depending on the heat output. The latter can be determined by measuring the flow rate of the product on the coil by the sensor 5, the temperature of the product at the inlet to the furnace by the sensor b, and the exit from the furnace by the sensor 7. The task in the comparison element 8 can come, for example, in the form of the required temperature t at the outlet of the raw material from the furnace. The controller 9 through the actuator 10 sets the required amount of gas supply to the chamber. Air supply to the chambers is carried out from a common duct, depending on

the measured gas flow rates using the sensor 11 and air using the sensor 12. The signals from the latter arrive at the comparison elements 13 and act on the actuators 15 through the regulators 14

0 air supply through the chambers. The air pressure in the common line is maintained at the required level by a system consisting of a pressure sensor 16, a comparison element 17, a regulator 18, and an actuator mechanism 19, with the impact, as a rule, on the guiding apparatus of the blowers. The air supply correction system according to the method includes a sensor 20 for the content of oxygen in flue gases, a sensor 21 for the content of ao0 of hydrogen (products of underburning) in the flue gases. The signals from the latter are fed to the input of logic block 22, and the setting value of coefficient A is supplied to it. The outputs of the logical unit 22 are connected to

5 inputs of links 17 and 13 and through them periodically control the operation of the air supply regulators, both common and in chambers. The system implements the method as follows. Based on measured values

0 by the sensor 20 and 21 of oxygen and hydrogen (underburning products) in the logic block, the target function R is generated according to equation (1). A certain initial value of the target function Rw is stored in the memory of the block. By connecting periodically to the elements 13 and 17, the logic unit can vary to some extent by the air flow rate in the chambers and the total flow rate. In this variation mode, the current value of the function R is compared with that recorded in the memory RH. If subsequently the value of the function R becomes smaller, a step of change (correction step) of the air supply is formed and the current value of the function R is written 5 s in the memory instead of RH. After reaching a minimum by acting, for example, on the comparison elements 13, the system is connected to another control air supply element 13 to another chamber.

0 If, after acting on the second chamber, an even deeper minimum is reached, the logic unit is connected to element 17 and so periodically controls the air supply both through the chambers and the general one. Minimi

5, the function can be fixed by sequentially reversing the effects on elements 13 and 17.

The technical and economic efficiency of the proposed method in comparison with the prototype is ensured not only by maintaining the process parameters in predetermined limits, but also by finding the optimal mode of minimizing unreacted products. As a result, fuel and energy resources are saved by minimizing the oxygen component. The presence of the hydrogen component suppresses the process of nitrogen oxidation, and thus, the environmental feasibility of introducing the method and its advantages over the prototype is achieved.

o

(56) Copyright certificate of the USSR N 1038726.cl. F 23 N 3/00. 1983.

Oil, Gas, and Petrochemicals Abroad, N: 3. Translated Edition of US Magazines, 1987, p. 124.

USSR copyright certificate No. 1312326. cl. F 23 N 3/00, 1981.

USSR copyright certificate No. 939870, cl. F 23 N 3/00, 1982.

Oil, gas and petrochemicals abroad. No. 3. The translated edition of magazines of the USA, 1987. with. 103-104.

 FORMULA AND ZOBRETIN 15

METHOD FOR CONTROL OF TUBULAR FURNACE by adjusting for restrictions on productivity, rarefaction, oxygen retention in the combustion products, air distribution in the chambers and total air flow, characterized in that, in order to increase accuracy, the hydrogen content in the combustion products and in specified with

.twenty

I AM

constraints minimize the value of the function ft AOa + H2 „where Og, Na are the values of the measured concentrations of oxygen and hydrogen in the combustion products, A is a coefficient equal to 0.076-0.106, if the values of Og, H2 are measured in wt.%, and equal to 0.0108 - 0.0132. if the value is Oa. Not measured in vol.%, Successively changing the flow rate of total air and its distribution in the chambers.

Air